The present invention relates generally to the field of integrated circuits and their operation. More specifically, in one embodiment, the invention provides an improved logic device and method of its operation.
Logic devices and their methods of operation are well known to those of skill in the art. In particular, programmable logic devices have found wide application as a result of their combined low up-front cost and versatility to the user.
Altera's FLEX.RTM. and MAX.RTM. lines of programmable logic devices are among the most advanced and successful programmable logic devices in the industry. In the FLEX logic devices, a large matrix of logic elements is utilized. In a current commercial embodiment of such devices, each logic element includes a 4-input look-up table for performance of combinational logic and a register that provides for synchronous logic operation.
The logic elements are arranged in groups of, for example, eight logic elements to form larger logic array blocks (LABs). The LABs contain, among other things, a local interconnection structure. The local interconnections allow the outputs of the logic elements to be efficiently routed to other logic elements within a LAB. The various LABs are arranged on the device in a two dimensional array. The various LABs may be connected to each other and to pins of the device though continuous lines that run the entire length and width of the device.
The FLEX logic devices have met with substantial success and are considered pioneering in the area of programmable logic. While pioneering in the industry, certain limitations still remain. For example, it would be desirable to further increase the flexibility of the user and CAD software to program the device. In the presently available configurations, a particular signal may be blocked. That is, the signal cannot be routed out of a logic element or LAB because a path is not available. It is desirable to create a configuration in which blocked signals are minimized.
From the above, it is apparent that an improved logic device and method of its operation is desirable.